Heretofore, there has been widely employed an anti-friction bearing as a rotation support mechanism for a momentum ring utilizing a physical inertia of a rotating body, such as a spinning wheel for a gyroscope, a flywheel for controlling an attitude of a flying object, a flywheel for storing energy. However, as known, the anti-friction bearing involves a mechanical friction due to contact between a roller or a ball and a race. Especially, the mechanical friction has a great influence on control performance of the flywheel for controlling the attitude of the flying object and it has been a task of importance to minimize the friction. To accomplish the task, it is generally required to employ an anti-friction bearing having a size as small as possible. On the other hand, the rotation support mechanism must inevitably have a large structure at a portion around a rotation axis because of requirements for strength and accuracy and a mass is centered on that portion so that a major portion of the entire mass of the momentum ring is located there. Because of this, there is a limit in structure to increase an effective mass for enhancing inertia efficiency with respect to a rotation center.
Furthermore, if the rotation support mechanism is concentratedly provided around the rotation axis, it is necessary to employ an anti-friciton bearing of a large size to increase support rigidity with respect to the rotation axis against an external force. This requirement is incompatible with the requirement that the anti-friction bearing of smaller size be employed to reduce the mechanical friction.
Recently, a non-contact bearing utilizing a magnetic force has been used practically as the rotation support mechanism and produced satisfactory results in eliminating the mechanical friction. However, the known structure employing this type of support mechanism has a magnetic bearing mechanism at a central portion of the momentum ring as in the conventional anti-friction bearing support mechanism. This structure is effective for elimination of the mechanical friction, but it does not bring the intended result of effective distribution of a mass contributive to the support rigidity and the inertia efficiency for the rotation center.